I. Field of the Disclosure
The invention relates to electronic communications. More particularly, the invention relates to methods and apparatus for calibrating a receiver to improve performance.
II. Description of Related Art
Radio Frequency (RF) receivers often process received signals in quadrature signal paths. The receiver can receive an RF signal and recover or otherwise generate In-phase (I) and Quadrature (Q) signal components. Often, the receiver will generate the I and Q signal components in conjunction with frequency translation.
An imbalance in the processing of the I and Q signal components results in a sideband when the I and Q signals are combined. The level of the sideband can be reduced by matching or otherwise calibrating the signal processing in the I and Q signal paths. However, matching the phase and gains of the I and Q signal paths is complicated when the receiver is configured to support a wide range if input frequencies. It is difficult to match the gains in the I and Q signal paths across a wide range of frequencies. Similarly, it is difficult to match the phase responses of the I and Q signal paths.
The differences in the gain and phase responses of the I and Q signal paths may be attributable to variations in the frequency conversion stages used to generate the I and Q signal components. Therefore, not only do the I and Q signal paths need to be closely matched, but they may need to compensate for differences in the I and Q signal components produced by a frequency conversion stage.
It is desirable to maintain the gain and phase response of the I and Q signal processing paths in order to reduce or otherwise minimize the sideband that results from an amplitude or phase imbalance. Further, it is desirable to reduce the contribution from a sideband over a wide frequency range supported by a receiver.
The literature for related fields includes the following:    [1] R. Montemayor and B. Razavi, “A Self-Calibrating 900-MHz CMOS Image-Reject Receiver,” Proc. Eur. Solid-State Circuits Conf., September 2000., pp. 292-295.    [2] L. Der and B. Razavi, “A 2-GHz CMOS Image-Reject Receiver With LMS Calibration,” IEEE J. Solid-State Circuits, Vol. 38, No. 2, February 2003, pp. 167-175.    [3] M. Elmala and S. Embabi, “Calibration of Phase and Gain Mismatches in Weaver Image-Reject Receiver,” IEEE J. Solid-State Circuits, Vol. 39, No. 2, February 2004, pp. 283-289.